The present invention provides a spiral-wound membrane module design for various membrane filtration techniques having significantly reduced fluid flow resistance in the feed stream path. Specifically, the inventive spiral-wound membrane module is designed having a corrugated entrance and exit spacers together over less than 10% of the length of the spiral wound module and a stiffener sheet wound to provide for uniform feed channel gap width.
In the field of pressure-driven membrane separations (e.g., ultrafiltration, reverse osmosis, nanofiltration) there is frequently a problem of membrane fouling from contamination of other dissolved and suspended solids in feed streams. This kind of membrane separation has been used, for example, in apple juice clarification, waste water treatment, cheese whey desalting, potable water production, oil-water emulsion separation, etc.). This problem has been addressed in a variety of ways. For feed streams that are not fouling, hollow fiber membrane module are most efficient and cost effective means of separation. However, hollow fiber membrane designs will foul most easily and cannot be used for the majority of feed streams in industrial processing or waste treatment due to fouling problems.
The next most expensive membrane design in terms of providing the greatest membrane surface area in a vessel per cost is a spiral wound configuration. In a spiral wound configuration, a permeate spacer, a feed spacer and two membranes are wrapped around a perforated tube and glued in place. The membranes are wound between the feed spacer and the permeate spacer. Feed fluid is forced to flow longitudinally through the module through the feed spacer, and fluid passing through the membranes flows inward in a spiral through the permeate spacer to the center tube. To prevent feed fluid from entering the permeate spacer, the two membranes are glued to each other along their edges with the permeate spacer captured between them. The feed spacer remains unglued. A diagram of a cross-section of three wraps of a standard module is shown in FIG. 1. Module assemblies are wound up to a desired diameter and the outsides are sealed. In operation, multiple modules are placed in a tubular housing and fluid is pumped through them in series. The center tubes are plumbed together to allow removal of generated permeate.
Spiral wound membrane designs have been used successfully but can also foul with higher fouling feed streams. The fouling problem in standard spiral wound membranes is often due to the nature of the feed spacer that is required to be located through each of the feed channels. In addition, the presence of the feed spacer creates significant resistance to fluid flow. A typical feed spacer is a polymeric porous net-like material that the feed must be forced through in the longitudinal direction (i.e., the length) of the spiral wound membrane. Therefore, spiral wound membrane designs can also have fouling problems in the feed spacer and membrane and incur significant fluid dynamic problems due to resistance of the feed spacer. However, spiral wound designs are less expensive than alternatives for only less-fouling feed streams.
For the most fouling feed streams (for examples, solutions containing high levels of suspended solids or tend to form gels upon concentration) a tubular design membrane module has been designed. A tubular design provides the least amount of membrane surface area per module length, and is most expensive to manufacture due to labor intensive procedures for xe2x80x9cpottingxe2x80x9d the tubular membranes within a module. Moreover, the inlet and outlet chambers associated with tubular designs are also most expensive. Therefore, there is a need in the art to replace the tubular design with a less expensive design and still be able to process highly fouling feed streams. The present invention was made to replace the tubular design with a spiral wound design for those feed streams that could not otherwise be processed (economically) in standard membrane modules having feed spacer designs.
The present invention provides a spiral wound membrane module having a length and a radius and a circular cross section, having reduced fluid flow resistance, comprising:
(a) an envelope sandwich having a width equal to the length of the membrane module and comprising a layer of membrane next to a layer of permeate spacer material next to a stiffener means, next to a layer of permeate spacer material next to a layer of membrane, and wherein the envelope sandwich is wrapped increasing the radius of the membrane module; and
(b) a structural assembly located between each wrap of the envelope sandwich to provide an open path for each feed chamber throughout the length of the membrane module.
Preferably, the stiffener means is composed of a hard shell sheet or an extruded or calendered rib. Most preferably, a rib stiffener means run in the same direction as permeate flow and provide permeate channels. Preferably, the structural assembly extends no more than 10% of the length of the membrane module. Preferably, the structural assembly is located at both ends of the membrane module. Preferably, the membrane module further comprises a perforated or porous tube extended throughout the length of the membrane module and located axially around a cylinder axis of the membrane module. Most preferably, the perforated or porous tube is used to collect permeate.
Preferably, the stiffener in the form of a sheet is made from a rigid sheet having a thickness of from about 0.1 mm to about 3 mm, most preferably from about 0.5 mm to about 1 mm. Preferably, the stiffener in the form of a sheet is made from a rigid material selected from the group consisting of PVC (polyvinyl chloride), C-PVC (chlorinated polyvinyl chloride) polypropylene, polyethylene, acrylic, stainless steel, copper, tin, and aluminum. Most preferably, the stiffener sheet is polyethylene for food uses or PVC for non-food uses, or C-PVC for high temperature uses. Preferably, the structural assembly is a corrugated pattern ribbon. Preferably, the structural assembly is a rigid material, wherein the rigid material is selected from the group consisting of polyethylene, stainless steel, aluminum, acrylic, and polycarbonate.
The present invention further provides a process for making a spiral wound membrane module having a length and a radius and a circular cross section, having reduced fluid flow resistance, comprising
(a) assembling an envelope sandwich having a width equal to the length of the membrane module and comprising a layer of membrane next to a layer of permeate spacer material next to a layer of stiffener means next to a layer of permeate spacer material next to a layer of membrane, and wherein the envelope sandwich is wrapped increasing the radius of the membrane module;
(b) assembling a structural assembly on either end of the envelope sandwich; and
(c) wrapping the envelope sandwich having the structural assembly and glue to form the spiral wound membrane module.
Preferably, the stiffener means is composed of a hard shell sheet or an extruded or calendered rib. Most preferably, a rib stiffener means run in the same direction as permeate flow and provide permeate channels. Preferably, the process further comprises before step (c) adding glue to either end of the envelope sandwich. Preferably, the structural assembly extends no more than 10% of the length of the membrane module. Preferably, the membrane module further comprises a perforated or porous tube extending throughout the length of the membrane module and located axially around a cylinder axis of the membrane module and upon which the sandwich assembly is wrapped.
Preferably, the stiffener in the form of a sheet is made from a rigid sheet having a thickness of from about 0.1 mm to about 3 mm, most preferably from about 0.5 mm to about 1 mm. Preferably, the stiffener in the form of a sheet is made from a rigid material selected from the group consisting of PVC (polyvinyl chloride), C-PVC (chlorinated polyvinyl chloride) polypropylene, polyethylene, acrylic, stainless steel, copper, tin, and aluminum. Most preferably, the stiffener sheet is polyethylene for food uses or PVC for non-food uses, or C-PVC for high temperature uses. Preferably, the structural assembly is a corrugated pattern ribbon. Preferably, the structural assembly is a rigid material, wherein the rigid material is selected from the group consisting of polyethylene, stainless steel, aluminum, acrylic, and polycarbonate.